Mendeleev Communications Electronic Version, Issue 1, 2000 (pp. 1–42) Synthesis, molecular and crystal structure of a tricarbonylchromium complex of 7-(2-phenyl-o-carboran-1-yl)cyclohepta-1,3,5-triene Valery N. Kalinin,*a Igor V. Shishkov,a Sergey K. Moiseev,a Pavel V. Petrovskii,a Zoya A. Starikovaa and Dae Dong Sungb a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation.Fax: +7 095 135 6549; e-mail: vkalin@ineos.ac.ru b Department of Chemistry, Dong-A University, Saha-Gu, Pusan, 604-714, Korea. E-mail: ddsung@seunghak.donga.ac.kr DOI: 10.1070/MC2000v010n01ABEH001184 The reaction of substituted 1-lithio-o-carboranes with tropylium tetrafluoroborate produces 7-(o-carboran-1-yl)cyclohepta-1,3,5- trienes, which can also be obtained by decomplexation of the corresponding tricarbonylchromium complexes prepared from 1-lithio-o-carboranes and [(C7H7)Cr(CO)3]+BF4 – .Higher-order cycloaddition reactions are a promising approach to the preparation of otherwise hardly available carbocyclic compounds. 1 Cyclohepta-1,3,5-triene derivatives are very effective 6p-participants in [6p + 4p] and [6p +2p] cycloaddition reactions. 2,3 Tricarbonylchromium complexes of substituted cycloheptatrienes can also be involved in the reaction.4,5 The complexes can be prepared by reactions of a tropylium tricarbonylchromium complex with the corresponding nucleophiles.6 Their tricarbonylchromium complexes can also enter the reactions, and the cycloaddition products obtained differ in structure from those prepared from the uncomplexed starting cyclohepta-1,3,5-triene derivatives.1,7 The only cycloheptatriene derivative described to date is 7-(2-methyl-o-carboran-1-yl)cyclohepta-1,3,5-triene,† which was obtained from 1-lithio-2-methyl-o-carborane and 7-methoxycyclohepta- 1,3,5-triene.8 Here, we describe a common method for preparation of 7-(o- or m-carboran-1-yl)cyclohepta-1,3,5- triene derivatives along with their h6-tricarbonylchromium complexes.† The terms ‘o-carborane’ and ‘m-carborane’ denote 1,2- and 1,7-dicarba- closo-dodecaborane(12), respectively. We found that 1-lithio-2-R-o-carboranes 1a,b readily react with tropylium tetrafluoroborate 2 in a diethyl ether–hexane solution to form corresponding 7-(2-R-o-carboran-1-yl)cyclohepta- 1,3,5-trienes 5a,b in good yields (Scheme 1).‡ Only one regioisomer of product 5 was isolated in each case.The corresponding 1H NMR spectra (in CDCl3) show three signals attributed to three pairs of the alkenyl hydrogens and a peak of one nonalkenyl hydrogen of the cycloheptatrienyl ring. These data unambiguously indicate that the carboranyl moiety in pro-duct 5 is attached to the 7-position of cyclohepta-1,3,5- triene.That is, the carboranyl substituent occupies the allyl position regarding the carbon–carbon double bond system of the ring. This is important for cycloaddition reactions because a rather strong electron-accepting effect and the presence of a bulk carboranyl group lead to a decrease of the reactivity of the carborane-connected carbon–carbon double bonds in the cycloaddition processes.9 A reaction of lithiated carboranes 1a–d with [(C7H7)Cr- (CO)3]+BF4 – was used to prepare the tricarbonylchromium complexes of o- and m-carboranyl derivatives of cyclohepta-1,3,5- triene 4a–d.§ The chromium complexes obtained in 65–75% yields are red air-stable compounds slowly decomposing in solution. ‡ General procedure for preparation of 5a,b.To a solution of 1a or 1b (0.01 mmol) in dry diethyl ether (30 ml) a hexane solution of BunLi (0.01 mmol) was added. The mixture was stirred at room temperature for 30 min. Next, compound 2 (0.01 mmol) was added. After additional vigorous stirring for 2.5–3 h, the reaction mixture was quenched with water (20 ml). The organic layer was separated and dried with anhydrous sodium sulfate.The solvent was removed under reduced pressure, and column chromatography (silica gel, diethyl ether–petroleum ether) of the residue followed by recrystallization from hexane gave 5a (85%) or 5b (80%). § Complex 4c was isolated in 2–3% yield. C(16) C(15) C(17) C(14) C(18) C(13) C(1) H(3') H(6') C(2) B(11) B(12) B(10) B(9) B(8) B(6) B(5) B(4) B(3) C(19) H(19) C(25) C(24) C(23) C(22) C(21) C(20) Cr(1) C(27) O(27) C(26) O(26) C(28) O(28) Figure 1 General view of a molecule of 4b.Selected bond lengths (Å): Cr(1)–C(20) 2.323(8), Cr(1)–C(21) 2.215(7), Cr(1)–C(22) 2.198(8), Cr(1)– C(23) 2.212(7), Cr(1)–C(24) 2.218(7), Cr(1)–C(25) 2.295(6), C(2)–C(19) 1.550(9), C(1)–C(2) 1.700(9), C(1)–C(13) 1.522(9), C(1)–B(3) 1.680(11), C(1)–B(4) 1.679(9), C(1)–B(5) 1.695(11), C(1)–B(6) 1.737(8), C(2)–B(3) 1.723(9), C(2)–B(6) 1.711(11), C(2)–B(7) 1.741(10), C(2)–B(11) 1.708(10), Cr(1)···C(19) 2.825(8); selected bond angles (°): C(13)–C(1)–C(2) 118.8(5), C(1)–C(2)–C(19) 117.6(5), C(19)–C(20)–C(21) 127.3(7), C(19)–C(25)– C(24) 127.4(7), C(20)–C(19)–C(25) 108.8(6), Cr(1)–C(20)–C(19) 92.7(5), Cr(1)–C(25)–C19 93.9(4).H(20) BF4 RCB10H10CLi i RCB10H10CLi Cr(CO)3 BF4 RCB10H10C RCB10H10C ii Cr(CO)3 H 1 2 3 4 5 6 7 1 2 3 4 5 6 7 a R = o-Me b R = o-Ph c R = o-H d R = m-Me 1a,b 2 5a,b,d 4a–d iii, iv 1a–d 3 Scheme 1 Reagents and conditions: i, hexane–Et2O, 20 °C, 3 h; ii, hexane– Et2O, 20 °C, 10–20 min; iii, MeCN–THF (35:15); iv, (NH4)2Ce(NO3)6, H2O–MeCN (35:20).Mendeleev Communications Electronic Version, Issue 1, 2000 (pp. 1–42) An X-ray study of complex 4b¶ showed that the carboranyl moiety is attached to the cycloheptatrienyl ligand at the 7-position and has an exo orientation relative to the Cr(CO)3 group (Figure 1). 1H NMR spectra (in CDCl3) of compounds 4a–d unambiguously indicate that the carboranyl moiety is attached to the cyclohepta-1,3,5-triene ring at the 7-position. The tricarbonylchromium group can be easily removed from complexes 4a,b,d by the action of (NH4)2Ce(NO3)6 in a THF solution releasing free ligands 5a,b,d.Satisfactory analyses as well as IR and 1HNMR†† spectra were obtained for all 7-(carboran-1-yl)cyclohepta-1,3,5-triene derivatives and their h6-tricarbonylchromium complexes. ¶ Crystallographic data for 4b: C18H22B10CrO3, M = 446.46, orthorhombic crystals, spase group P212121, a = 8.292(2), b = 8.674(2), c = = 30.658(11) Å, V = 2205(1) Å3, z = 4, dcalc = 1.345 g cm–3, m(MoKa) = = 5.38 cm–1, F(000) = 912.The intensities of 3426 reflections were measured on a Siemens P3/PC diffractometer at –120 °C (lMoKa radiation, q/2q scan technique, 2q < 50°), and 3048 independent reflections were used in further calculations and refinement.The absolute conformation for the molecule of 4b was determined by calculation of the Flack parameter [k = 0.05(5)]. The structure was solved by a direct method and refined by a full-matrix least-squares technique against F2 in an anisotropic –isotropic approximation. The positions of hydrogen atoms were located from the difference Fourier syntheses. The refinement was converged to wR2 = 0.1633 and GOF = 0.974 for all 3023 independent reflections [R1 = 0.0565 was calculated against F for the 2143 independent reflections with I > 2s(I)].The number of the refined parameters is 377. All the calculations were performed using SHELXTL PLUS 5.0 on an IBM computer. Atomic coordinates, bond lengths, bond anlges and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ‘Notice to Authors’, Mendeleev Commun., Issue 1, 2000. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/58. †† 1H NMR spectra (400 MHz, CDCl3, d/ppm). 4a: 0.80–2.95 (m, 10H, B10H10), 2.05 (s, 3H, Me), 3.83 (m, 1H, 7-H), 3.64 (m, 2H, 1-H, 6-H), 5.04 (m, 2H, 2-H, 5-H), 6.03 (m, 2H, 3-H, 4-H). 4b: 0.9–3.30 (m, 10H, B10H10), 3.10–3.50 (m, 3H, 1-H, 6-H, 7-H), 4.94 (m, 2H, 2-H, 5-H), 5.96 (m, 2H, 3-H, 4-H), 7.23–7.95 (m, 5H, Ph). 4c: 0.90–2.85 (m, 10H, B10H10), 3.16 (br. s, 1H, HCCB10H10), 3.66 (m, 2H, 1-H, 6-H), 4.02 (t, 1H, 7-H, 3J7,1 = 3J6,7 = 8.8 Hz), 5.00 (m, 2H, 2-H, 5-H), 5.95–6.05 (m, 2H, 3-H, 4-H). 4d: 1.15–3.18 (m, 10H, B10H10), 1.59 (s, 3H, Me), 3.59–3.70 (m, 3H, 1-H, 6-H, 7-H), 4.91–5.00 (m, 2H, 2-H, 5-H), 5.95 (m, 2H, 3-H, 4-H). 5a: 1.00–3.75 (m, 10H, B10H10), 1.65 (t, 1H, 7-H, 3J6,7 = 3J7,1 = 6.0 Hz), 1.80 (s, 3H, Me), 5.38 (dd, 2H, 1-H, 6-H, 3J1,7 = 3J6,7 = 6.0 Hz, 3J1,2 = = 3J5,6 = 8.8 Hz), 6.26 (m, 2H, 2-H, 5-H), 6.77 (m, 2H, 3-H, 4-H). 5b: 1.13 (t, 1H, 7-H, 3J1,7 = 3J6,7 = 6.0 Hz), 1.80–3.70 (m, 10H, B10H10), 5.32 (dd, 2H, 1-H, 6-H, 3J1,2 = 3J5,6 = 8.8Hz, 3J6,7 = 3J1,7 = 6.0 Hz), 6.04 (m, 2H, 2-H, 5-H), 6.42 (m, 2H, 3-H, 4-H, 3J3,2 = 3J4,5 = 3.2 Hz), 7.23 (t, 2H, m-HPh, J 7.6 Hz), 7.34 (t, 1H, p-HPh, J 7.6 Hz), 7.44 (t, 2H, o-HPh, J 7.6 Hz). 5d: 1.05–3.65 (m, 10H, B10H10), 1.72 (s, 3H, Me), 1.68–1.78 (m, 1H, 7-H), 5.26 (dd, 2H, 1-H, 6-H, 3J1,2 = 3J5,6 = 8.8 Hz, 3J1,7 = 3J6,7 = 6.0 Hz), 6.16 (m, 2H, 2-H, 5-H), 6.70 (m, 2H, 3-H, 4-H).This work was supported by the Russian Foundation for Basic Research (grant nos. 97-03-33783a and 99-03-32899) and by the Scientific Training Centres on the Chemistry of Organometallic Compounds and Biomedical Chemistry (grant nos. 234 and K0599, the ‘Integratsiya’ Special Federal Program). 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